1. Field of the Invention
The present invention relates to a method and an apparatus for judging whether a metallic cable for communication is In an active status capable of serving for the communication or not.
2. Description of the Background Art
A worker for laying the metallic cable for communication (referred hereafter simply as a cable) through underground or space is required to .judge whether each cable is an active line which is capable of transmitting signals by being power supplied from a terminal device, or a dead line which is not in the active status, prior to the work for cutting or removing the unnecessary cables. In such a work, when the active line is cut by mistake due to the erroneous .judgement of the active line, some trouble can be caused to the system connected with the erroneously cut active line or the communication service with respect to the terminal contained in that system is interrupted.
Conventionally, there are the following three methods for judging whether the cable to be a target of the above described work is an active line or not.
The first method is to confirm a physically cut off state of the cable at a connection point of a terminal device or a relay point of the cable by the visual inspection, and distinguishably marking the cable to be a target of cable cutting or removing operation by attaching tags along that cable.
The second method is to transmit special monitor signal through the cable From a connection point of a terminal device or a relay point of the cable, and determining a cable located at the working site from which the monitor signal can be received through a receiver device, so as to distinguish the cable to be cut or removed as that From which the monitor signal cannot be received.
The third method is to detect the contact of a cutting blade of a cable cutter used in the cable cutting operation with the conductive cable core, and stopping the cable cutting operation by utilizing the electromagnetic lock mechanism.
However, these conventionally known methods have been associated with the following problems.
Namely, in the first method, it is necessary to confirm the cable to be marked by the visual inspection many times, especially when a position at which a physically cut off state of the cable is confirmed and the cable cutting or removing work site are distanced. As a result, there is a possibility for the other cable to be erroneously marked, especially in a section at which numerous cables are laid densely, and many operation steps are required for the cable cutting or removing operation.
In the second method, the receiver device for detecting the monitor signal is very expensive, and its significantly large mechanical size has been severely limiting a size of the workable working site or interfering with the working performance of the worker. Moreover, in order to detach a oscillator device for transmitting the monitor signal after the completion of the cable cutting or removing work, it has been necessary for the worker to go back from the cable cutting or removing work site to the location at which the oscillator device has been attached at a beginning of the cable cutting or removing work.
In the third method, the specially designed cable cutter capable of functioning In the above described manner is very expensive, and the judgement of the active/dead line cannot be made without cutting through the outer covering of the cable, so that the cable is damaged even when the cutting operation Is stopped by the electromagnetic lock mechanism, and therefor there has been a need to replace the damaged cable with a new one whenever the erroneous cutting of the active line Is prevented by the electromagnetic lock mechanism.